Such a metal tubular structure is for example of the type consisting of a trellis of tubular elements. It then consists of a plurality of metal tubular sections assembled together.
The shape of the metal structure is generally adapted to its use. It can thus form a mast supporting radio transmission aerials, in particular for radio broadcasting, or an offshore structure etc.
In all cases, such a structure is subjected to various forces. If it consists for example of a radio transmission mast, these forces comprise in particular the effect of the weight of the aerials positioned on the mast as well as the effect of external actions such as the weight of snow, wind pressure, seismic phenomena etc.
The structures are therefore dimensioned, when designed, to withstand service loads and accidental loads, according to the equipment installed on these structures, for example the number and type of aerials surmounting a mast.
Technological developments and operating constraints sometimes lead to the replacement of apparatuses used by different items of equipment or of the addition of others. Operating loads and the action of external stresses therefore become modified by these, with the consequence that it is necessary to reinforce the structure in situ or to replace it.
Known reinforcing methods consist of adding or replacing elements of the metal structure in situ so as to increase the metal sections in the desired proportions in order to meet new stresses. This restructuring process is generally complex, in particular in the region of assembly points of the structure. It moreover involves disturbance to, or even the stoppage of, operations associated with demounting the installed equipment, for example aerials, during the period of operations. These stoppages are costly and very restricting for the operator. Moreover, these reinforcements modify the external appearance of the structure and can therefore make it necessary to obtain prior work authorization that can considerably retard operations.
WO 2004/038106 discloses another method for reinforcing a metal tubular structure, wherein a metal reinforcing layer is placed at a distance from an internal surface of the tubular structure so as to form a cavity between said reinforcing layer and the tubular structure. Plastic or polymer is injected into this cavity, so that, after curing, it adheres to the reinforcing layer and to the internal surface of the tubular structure.
Such an arrangement provides a reinforcement of the metal tubular structure when bending. On the other hand, it in no way improves the tensile strength and/or compressive strength that are however most significant as regards such a structure.